Spinning of fibres



Feb. 3, 1970 P. L. l. CARR 3,492,591

- SPINNING 0F FIBRES I Filed Aug. 19. 1966 2 Sheets-Sheet 1 v mun /raw?PQWZQMBm/YZYWMoCZ/W yzumwwg /wzw United States Patent 3,492,691 SPINNING0F FIBRES Paul Lambton Inwood Carr, Harrogate, England, assignor toImperial Chemical Industries Limited, London, England, a corporation ofGreat Britain Filed Aug. 19, 1966, Ser. No. 573,532 Claims priority,application Great Britain, Aug. 20,1965, 35,785/ 65 Int. Cl. D01d 5/08,11/00 US. Cl. 18-8 1 Claim ABSTRACT OF THE DISCLOSURE The uniformity ofmelt spun polymer filaments is improved by surrounding the moltenfilaments with series of axially spaced-apart collars which togetherwith the effect of the moving filaments induce a laminar flow to theambient air which flows inwardly toward the filaments and then along thepath of the filaments.

The present invention relates to the melt-spinning of fibre-formingpolymers.

According to the present invention we provide a process for the spinningof a fibre-forming polymer wherein the said polymer in the liquid stateis forced through one or a plurality of holes in a spinneret plate, thestream or streams of polymer formed thereby travelling substantiallyvertically downwards from the spinneret plate and solidifying as it, orthey, pass through the ambient fluid, a flow of ambient fluid beinginduced by the movement of the stream or streams of polymer initiallytowards the stream or group of streams of polymer and then following thepath of the, or of each, polymer stream, deflecting means being disposedat intervals along the length of the path of the stream or streams ofpolymer whereby the flow of the ambient fluid towards the stream or eachstream, of polymer and thereafter following the path of the, or of each,stream of polymer, is a stable laminar flow, the said conditions ofstable laminar flow persisting until the temperature of the, or of each,stream of polymer falls to the solidification point.

By the term ambient fluid, we mean gases and vapours which arechemically inert towards the polymer; the most convenient gas to use isair.

In the formation of a filament by melt-spinning, a polymer at atemperature above its melting point is forced through a hole to form anarrow stream of molten polymer. This stream of polymer normally travelsvertically downwards and is acted upon by a force in a downwardsdirection along the length of the stream in such a manner as toattenuate the stream as it cools and eventually solidifies. Thus thespeed of movement of the polymer stream along its length increases withdistance from the spinneret and becomes quite high at a moderatedistance from the exit of the spinneret hole.

As the stream of polymer moves away from the exit of the spinneret hole,it loses heat to the surrounding air, resulting in a local zone of airof temperature higher than the surroundings. The air immediatelyadjacent to the polymer stream will be carried along with the polymerstream and more distant layers will be carried along to a diminishingextent. The air which is carried along with the polymer stream, isreplaced by inward flow of air towards the polymer stream.

The uses to which filaments are put demand a high degree of uniformityin the filaments; this in turn demands a high degree of uniformity ofthe thermal history of all parts of the filament. That is any particularpoint in the final filament must have been subice jected tosubstantially the same profile of temperature change as any other pointat the same distance from the long axis of the filament.

The system of moving polymer stream and layers of air, under suchcircumstances is, however, inherently unstable, partly in view of theonset of turbulent flow conditions at sufficiently high velocity of thepolymer stream and partly due to interaction of the moving layers withthe incoming flow of air towards the polymer stream.

We have found that when it is ensured that the flow of air towards thestream of polymer is a laminar flow, and therefore contains no eddies,then gerater stability is conferred on the system, and the airtemperature gradient from the surface of the polymer stream outwards atany given distance from the exit of the spinneret hole tends to remainmuch more constant than it otherwise would.

Normally in the manufacture of filaments by meltspinning, a spinneretplate is used in which are bored a series of holes in some regulargeometrical pattern, for example a circle or oval. In such a case, theflow of air induced towards the polymer streams must come fromessentially one side of each polymer stream, that is the side away fromthe volume which is substantially enclosed by the polymer streams. It istherefore the inflow of air from this side which must be controlled.

The need for controlling the flow of air towards the polymer streamarises from the presence of adverse movement in the surrounding air,which may arise from locally moving bodies or from convection currents.Convection currents may, for example, be induced by the heated airleaving the vicinity of the polymer stream at points more distant fromthe exit from the spinneret hole and where the polymer stream hassolidified.

We have found that the desired conditions of laminar flow of air towardsthe polymer streams can be ensured by, for example, a series of membersso constructed and disposed that, while they permit the free flow of airtowards and finally into the direction of motion of the polymer stream,they do not permit the interference with such flow by non-laminar flows.

The members may suitably form a series of control surfaces, of whichthere should be at least two. The control surfaces may be in the form ofcomplete collars surrounding the group of polymer streams or of morethan one member substantially delineating a collar. The collars may, forexample, be in the form of annular discs, but are preferably of suchshape that the parts further away from the polymer streams are atprogressively higher levels with a smooth graduation in order tominimize the entry of rising currents of air between successive controlsurfaces. Such a formation of the control surfaces also minimizes thebreaking away of the zone of air adjacent to the polymer streams andmoving with them. The collars may advantageously be in the form of thesurface of a conical frustum with the wider part uppermost, or of thesurface generated by the rotation of a portion of an exponential curveabout the abscissa.

The plurality of control surfaces may comprise a single member; suchmember may, for example be a suitably offset Archimedean screw with aleast two complete turns.

A greater number than two control surfaces produces an improvement,albeit with diminishing magnitude of improvement with number. Below aseparation of about 5 mm., the effect of air drag impairs the necessaryfree flow of air. At separation greater than about mm., the requisiteeffect in producing a stable laminar flow is not observed, and theresults produced are inferior to those for a lesser separation.

. to arrange a series of closely spaced obstructions, for

example a gauze, across the threshold delineated by the adjacent outeredges of the control surfaces. Such an arrangement has the effect ofsmoothing out turbulence in the air stream as it starts to flow betweenthe adjacent control surfaces, and thus facilitates the establishment oflaminar flow.

The mmeber or members comprising each control surface may be ofcontinuous laminar form or may be pierced by a number of apertures. Thenumber and disposition of such apertures should not be such as to permitthe passage freely through them of the ambient fluid in more than aminor amount compared to the total flow.

The construction and disposition of the control surfaces should be suchthat the edge of each control surface nearer to the polymer stream isdistant by a predetermined amount.

The predetermined amount is controlled mainly by the nature of theambient fluid and to only a minor extent by the linear speed of thepolymer stream and should be such that no part of the member isappreciably nearer to the polymer stream than the point at which theinduced air-flow in the direction of motion of the polymer stream isfrom about 1% to about of the value of the linear rate of motion of thepolymer stream. This value may be calculated on the basis of normalphysical principles. Using air as the ambient fluid, a suitable distancebetween a control surface and the polymer stream may be as small asabout 4 mm. but should not exceed about 30 mm. In order to produce auseful effect, a control surface should extend radially for a distanceof at least about mm. The inner edge of the control surface mayadvantageously be conformed so that the distance from it of each of theoutermost of the polymer streams is approximately equal.

The disposition ,of the control surfaces along the length of the polymerstreams should be such as will ensure the closest approximation tolaminar flow in the fluid flow induced towards the polymer streams. Theeffectiveness of the disposition can be checked by the observation ofthe movement of smoke trails introduced into the vicinity of the controlsurfaces.

When melt-spinning is carried out according to the process of ourinvention, that is with laminar flow of the ambient fluid towards thepolymer streams and thereafter along with the polymer streams, theconditions are such that the rate of heat transfer from the polymerstreams to the ambient fluid is minimized. Thus for a given size ofpolymer stream, the use of the process of our invention results in theminimum degree of orientation, other things being equal. This ismanifested in the spun fibre by its possessing a relatively lowbirefringence. In normal use of melt-spin fibres a predetermined degreeof orientation has to be arrived at in order that the fibre shall havethe desired useful properties. In order to achieve the predetermineddegree of orientation, cold drawing is resorted to, that is drawing of atemperature below the melting point of the polymer of which the fibre iscomposed. In this cold drawing step it is found that fibres as spunhaving a low degree of orientation can successfully be drawn to a higherdraw ratio than fibres having a high degree of orientation as spun.Thus, to obtain a particular final drawn denier, a fibre of low degreeof orientation as spun may be of higher denier than when the as-punorientation is higher. Thus if one considers the combined process ofspinning a fibre followed by drawing it to produce a particular finaldrawn denier in the fibre, the process of our invention permits thespinning of a higher denier fibre. Or alternatively our inventionpermits an increase in the windup speed and increase in the throughputper spinneret hole for the same degree of orientation.

In order that the process of our invention may be the more fullycomprehended, we give hereinafter a descrip tion of a specificembodiment by Way of example and with reference to the accompanyingdrawings in which:

FIGURE 1 shows a cross-section in a vertical plane through the centre ofa spinneret plate, of a series of deflecting members. A multiplicity ofpolymer streams is shown for clarity, although such a section would notshow more than two;

FIGURE 2 shows a plan view 0 fthe uppermost deflecting member;

FIGURE 3 is a representation of a threadline being formed under theconditions of our invention;

FIGURE 4 is one representation of a threadline being formed underconditions outside our invention.

Referring to FIGURES 1 and 2, a series of six identical members 5,constructed from inch thick tinned steel and each consisting of aportion 6 in the form of the curved surface of a right conical frustumof conical angle base 7 cm. diameter and top 1.75 cm. diameter, integralwith an annular disc 7 of outside diameter 10 cm. and internal diameter7 cm., are held in fixed juxtaposition, with the annular discs 5 beingin parallel planes and the bases of the conical frustal portions 6facing all in the same direction, by means of rods 7, 8 and 9 which arethreaded and pass through holes of which there are three equidistantbored through each annular disc 5 with centres 0.5 cm. from the outeredge of the disc 5. The members are held in their relative positions (1/2 inches separation between adjacent annular parts) by means of nuts 10screwed on to the threaded rods 7, 8 and 9.

In use the assembly of members is disposed with the rods 7, 8 and 9vertical and the bases of the conical frustal portions 6 uppermost. Theuppermost member has its annular part at 2.5 cm. from the spinneretplate. The assembly hereinbefore described was for use with a spinneretplate in which were bored 15 spinning holes of .009 inch diameter withcentres on a circle of 1 cm. diameter. The assembly was so positionedwith respect to the streams of polymer issuing from the spinning holesthat each polymer stream was approximately 4 mm. from the nearest pointof each of the conical frustal portions 6.

EXAMPLE 1 (A) Using the described apparatus, poly(ethyleneterephthalate) of viscosity ratio 1.7 as measured in orthochlorophenolsolution at 1% concentration at 25 C., and containing 0.5% of titaniumdioxide delustrant, was melt-spun at a temperature of 290 C. at athroughput per hole of 0.4 g. per minute through 15 circular holes of0.009 inch diameter on a circle of radius 0.25 inch (0.635 cm.). Thefibre was wound up at 1,500 cm. per second. The coefiicient of variationof the resultant yarn was determined by weighing 25 lengths of yarn of10 metres length and calculating the coeflicient in the usual manner.The coeflicient of variation was found to be 0.66%.

(B) For comparison, spinning of exactly similar polymer was carried outunder exactly the same conditions omitting only the assembly of membersas hereinbefore described. Measurement of the coefficient of variationof the resultant yarn by the same method gave a value for thecoefficient of 1.2%.

EXAMPLE 2 Example 1A was repeated exactly with the single distinctionthat a cylinder of gauze was fitted around the assembly of members. Thegauze was of 32 meshes per inch and made of 30 gauge wire (BritishStandard Wire Gauge). The gauze cylinder was in contact with the outeredge of each member of the assembly of members and extended from thespinneret plate to the lowest of the members. Thus the induced flow ofambient air had to flow through the meshes of the gauze.

The yarn produced had a coeflicient of variation, measured as describedin Example 1A, of 0.4%.

EXAMPLE 3 (A) Poly(ethylene terephthalate) of viscosity ratio the sameas that used in Example 1, was spun through a single circular hole of0.009 inch diameter at a throughput per hole of 1.6 g. per minute. Thestream of molten polymer was led through the centre points of 1 cm.holes in the centre of a series of 7 cm. discs each disposedhorizontally in similar relation to that described for the members forExample 1. The resultant monofil was wound up at 1,500 cm. per second.The monofil was of 16 denier. This is product I.

(B) By Way of comparison, spinning was carried out exactly as describedin Example 3A with the exception that the series of discs was omitted.The monofil was of 16 denier. This is product II.

Comparison of the coefiicient of variation of the diameter of products Iand II showed an improvement of product I as compared with product II.Product I had coefficient of variation 2%, while product II hadcoeflicient of variation 5%.

EXAMPLE 4 (A) Using the apparatus of Example 1A, isotactic polypropyleneof viscosity ratio 2.8, as measured on a 1% solution indeccehydro-naphthalene at 135 (3., at a temperature of 285 C., at athroughput of 0.25 gm./min./hole through circular holes of diameter0.015 in. diameter (0.0381 cm.) with centres on a circle of radius 0.635cm. The yarn was wound up at 10 metres/sec. Using the assembly ofmembers as described in Example 1, the coeificient of variation of thespun yarn was 2.6%.

(B) By Way of comparison, Example 4A was repeated exactly with the onlydistinction that the assembly of members was omitted. The coefiicient ofvariation of the spun yarn was 4.3%.

EXAMPLE 5 (A) In this example the assembly of members employed was asfollows:

The number of members was 8 and all were of identical shape anddimensions similarly oriented and similarly disposed with relation toeach other and to the spinneret plate as shown in FIGURE 1. Each memberwas of the form described in connection with Example 1 with conicalangle 100, and base of conical frustum 12 cm. diameter. The top of theconical frustum being of 5.8 cm. diameter for the uppermost memberreducing by uniform stages to 5.2 cm. for the lowermost member. Thisvariation was in conformity with the convergence of the filaments to aguide 1.5 metres below the spinneret. The various members were spacedfrom adjacent members by 2.5 cm. A gauze cylinder was fitted round thedevice as described in Example 2. The uppermost member was 2.5 cm. fromthe spinneret plate. The device was fitted below a spinneret plate inwhich were bored spinneret holes of 0.009 inch diameter in a scatterpattern such that the overall diameter of the set of filaments wasinitially 5 cm. and the hole spacing was approximately 1 cm. Theassembly was positioned so that the clearance between the filaments andthe inner edge of each member was approximately 4 mms.

Poly(ethylene terephthalate) of viscosity ratio, as measured asdescribed in Example 1, 1.7 and containing 0.5% by weight of titaniumdioxide was spun under the following conditions:

Spinning temperatures C-.. 290 Throughput gms./mm./hole 1.14 20 holescatter spinneret as described.

Wind up speed ..-cms./sec 2100 The coeflicient of variation of theresultant yarn as measured by the Uster Evenness Tester was 1.3%.

(B) For comparison, the yarn was spun under exactly the same conditionsomitting the stabilization device. The coefiicient of variation was2.3%.

A further improvement in the stability of the air can be effected byincorporating vertical fins in the space between adjacent controlsurfaces. This is because disturbances in the flow are three dimensionaldisturbances.

EXAMPLE 6 The apparatus was as used in Example 5 with the singleexception that vertically and radially disposed laminar members wereplaced symmetrically between, and forming a bridge between, eachadjacent pair of members (5 of FIGURE 1) and between the uppermostmember 5 and the spinneret plate.

The coefficient of variation of the spun yarn using the stabilizationdevice with this modification was 1.1% measured as before in Example 5.

Our invention is applicable not only to an array of spinneret holes withradial symmetry but also to other configurations, for example, arectangular configuration.

EXAMPLE 7 (A) The apparatus used was as described in Example 6 with thedistinctions that the spinneret holes were 24 in number and that thespinneret holes were arranged in 6 straight rows of 4 forming arectangular pattern of overall dimensions 5 cm. x 2.2 cms. Thecoefficient of variation of the yarn spun using this apparatus was1.75%.

(B) By comparison using the same spinning apparatus as in 7A butomitting the apparatus to control the flow of ambient air thecoefficient of variation of the yarn spun was 2.6%.

By way of further explanation of the conditions pertaining in the use ofour invention, reference is made to FIG- URES 1 and 2. Referring toFIGURE 1, the threadline 1 moving away from the spinneret 2, under theconditions of our invention induces a flow of air inward as shown by thestreamlines and thence in stable laminar flow in the direction of motionof the threadline. The velocity profile of the induced air flow is shownat 4. The transition to turbulence, shown at 5, occurs beyond the pointwhere the threadline has solidified. Under these conditions the heattransfer at a point at a particular distance from the spinneret isconstant with time. Referring to FIGURE 2, under conditions outside ofour invention there is an unstable laminar region 6 which exhibits largelowfrequency fluctuations. This is partly due to natural convectioneffects resulting in the presence of warm air currents and partly due tovibration of the threadline itself, the fluctuations are also to someextent inherent in the geometry of the system. Early separation of theboundary layer, spiralling, and in fact any departure from axialsymmetry leads to a momentary increase in the local rate of cooling,leading to deviation from the desired steady conditions.

What I claim is:

1. Apparatus for melt spinning a fibre-forming polymer comprising: aspinneret for forming at least one stream of polymer travellingsubstantially vertically downwardly from said spinneret through theambient fluid in the vicinity of the stream; and ambient fluid controlmeans for inducing the ambient fluid to flow laminarly toward thepolymer stream and thereafter laminarly along the path of the polymerstream until the temperature of the stream falls to the solidificationpoint, said means including ambient fluid deflecting elements disposedat spaced-apart intervals along the length of the path of the stream,said deflecting elements being out of contact with and at leastpartially surrounding the polymer stream, said deflecting elements beingcollar-shaped annular discs having a central portion shaped as adepending converging conical frustum so as to define at least twoannular control surfaces each of which is shaped such that a pointmoving radially along the surface from the iner to the outer edge has atno time any downward component of motion, the inner edge of each controlsurface being spaced from the polymer stream not less than about 4 mm.and not more than about 30 mm., and each control surface extending atleast about 10 mm. from its inner to the outer edge has at no time anydownward surface by at least about 5 mm. and at most about 100 mm.

References Cited UNITED STATES PATENTS 9/1966 Massey et al. 4/1967Finzel et a1. 12/1967 Nommensen et a1.

JULIUS FROME, Primary Examiner J. H. WOO, Assistant Examiner us. 01.X.R.

